The thing is, though, that for a very long time in history Black communities have had a raw deal. If this were somehow the fault of other black communities, which is partly true, that's beside the point. Almost from the first day that Europeans arrived in the Americas they set up the systems to exploit, persecute, subjugate, etc, the locals and just generally treated them like some lower form of life. Later on in the process we ran out of local people to enslave and "had" to use some from Africa. With the help of willing tribal leaders, perhaps...
But this has in the long run meant something close to 350 years of essentially continuous slavery of non-white communities in Africa and the Americas, and a further 150 years or so after that of their descendants still being treated like second-class citizens. All because of their skin colour and because gun beats spear.
And this kind of discrimination is ongoing today. If such communities want to have a month each year to remember this, emphasise the past, and try to overcome the remaining barriers, what's the problem? One month of hearing about this a year? And you don't even have to listen, if you don't want to, beyond an occasional email that you can always delete, or leaflets that you could easily put in a bin if you aren't interested in reading them. For others, they have to put up with this their whole lives. Moaning about an email pales into nothingness by comparison.